Gas-filled electric discharge devices



Nov. 18, 1969 B. o. BAKER CAS-FILLED ELECTRIC DISCHARGE DEVICES Filed001'.. 9, 196'? Fig.2

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29 43 www u my wn Il m, 7 /l/ I u, a Ii 4C B\\.T n El I 5 n .3 l .vm/YA`.\\ b, .4 m f Wn .4 /f /a 3 .4| w nw E F 5 f E 2 Q United StatesPatent O U.S. Cl. 313-195 6 Claims ABSTRACT F THE DISCLOSURE Agas-filled electric discharge device having an apertured controlelectrode and a correspondingly apertured electrode between the controlelectrode and the anode which serves to prevent deterioration of theperformance of the device under hold-olf conditions due to erosion ofthe anode.

This invention relates to gas-lilled electric -discharge devices.

The invention relates particularly to gas-filled electric dischargedevices of the kind including an electrode structure including an anode,a cathode and a control electrode, dispose between the anode and thecathode, in which is provided at least one elongated aperture throughwhich the discharge between the anode and the cathode passes inoperation.

In this specification the term gas-filled is intended to includevapour-lilled.

In use of electric discharge devices of the kind specified the anode maybe subject to erosion due to high energy particles being swept intocollision with the anode. This phenomenon may occur in a thyratron, forexample, during the short period which elapses between the commencementof the discharge and the collapse of the anode to cathode voltage,during which period electrons from the region of the discharge may beaccelerated towards the anode. In a vapour-filled `device employed as arectitier, such erosion may occur due to positive ions being acceleratedtowards the anode during the non-conducting half cycle of the device,when the anode may be at a high negative potential with respect to thecathode.

-Whatever the cause, the resulting erosion produces irregularities inthe shape of the surface of the anode, and hence in the configuration ofthe electric eld between the anode and the cathode, and this may lead toa deterioration in the performance of the device when the device isnon-conducting.

It is an object of the present invention to provide an electricdischarge device of the kind specified wherein this difficulty isalleviated.

According to the present invention, in an electric discharge device ofthe kind specied there is disposed between the anode and said controlelectrode an additional electrode which is electrically insulated fromsaid control `electrode and in which, for each said aperture in thecontrol electrode, there is a corresponding aperture which is ofsubstantially the same size and shape as the corresponding aperture inthe control electrode, and which, in respect of the path of a dischargebetween the anode and the control electrode, is at least approximatelyin register with the corresponding aperture in the control electrode.

It will be appreciated that said anode may constitute the main anode ofthe device, that is the anode carrying the lead current of the device,or may constitute an auxiliary anode of the device, for example, anelectrode whose purpose is to increase the hold-0E voltage of thedevice.

Patented Nov. 18, 1969 One arrangement in accordance with the inventionwill now be described, by way of example, with reference to theaccompanying drawings in which:

FIGURE 1 is a sectional elevation of a thyratron having a forwardhold-olf voltage of 35 kilovolts and adapted to pass a peak current of5000 amps, and

FIGURE 2 is a plan view of an electrode of the thyratron.

The thyratron has a sealed envelope filled with deuterium at a pressureof 0.25 torr.

Referring to the drawing, the main body of the envelope is in the formof a hollow, generally cylindrical structure incorporating two tubularmetal members 1 and 2 of lengths 4.5 inches and 1.5 inches respectivelyand each having an internal diameter of 3.75 inches, apart from slightvariations in diameter for the purpose of providing locating shouldersat various positions. The two tubular members 1 and 2 are disposed inaxial alignment and communicate via a relatively short, narrow, tubularceramic section 3 of the envelope. At one end, the ceramic section 3 isjoined to the shorter tubular metal member 2 by means of a thin-walledtubular metal sealing ring 4 which at one end is sealed to the inneredge of a ange 5 extending inwardly from the adjacent end of the tubularmember 2, and at its other end is provided with an outwardly extendingflange 6 which is sandwiched between the adjacent end of the ceramicsection 3 and a ceramic backing ring 7. At its other end the ceramicsection 3 is joined to the longer tubular metal member 1 by means of athin-walled tubular metal sealing ring 8 having an inwardly extendingilange 9 at one end and an outwardly extending flange 10 at the otherend, the inwardly extending flange 9 being sandwiched between theadjacent end of the `ceramic section 3 and a ceramic backing ring 11 andthe outwardly extending flange 10 being' sealed to the face of aninwardly extending ange 12 provided at the adjacent end of the tubularmember 1.

To shield the inner surfaces of the ceramic section 3 and the backingring 11 from the discharge in operation, a short tubular metal member 13is disposed coaxially Within the ceramic section 3, this member 13 beingjoined at one end to the inner edge of the flange 12.

At its end remote from the ceramic section 3 of the envelope, the longertubular member 1 is sealed to an annular cup-shaped metal sealing ring14 which nests within and is sealed to a second annular cup-shaped metalsealing ring 15. T'he sealing ring 15 is sealed in turn to one end of aceramic ring 16 with the aid of a backing ring 17, and the other end ofthe ceramic ring 16 is sealed to one main face of an outwardly extendingflange 18 formed around the mouth of a cup-shaped metal member 19 Iwhosebase extends across the end of the main body of the envelope. The othermain face of the ange 18 is sealed to one end of a further ceramic ring20 whose other end is sealed with the aid of a backing ring 21 to acompartment 22 which serves to close this end of the envelope and whichhouses a replenisher for the gas iilling of the thyratron. Thereplenisher communicates with the interior of the main body of theenvelope via four apertures 23 in the end of the replenisher compartment22 and an aperture 24 formed through the base of the member 19.

At the end of the shorter tubular member 2 remote from the ceramicsection 3 of the envelope there is provided an inwardly extending ange25 to which a tubular ceramic member 26 is joined by means of athin-walled tubular metal sealing ring 27. The sealing ring 27 isprovided at one end with an outwardly extending flange 28 which issealed to the flange 25, and at its other end is provided with aninwardly extending flange 29 which is sandwiched between the end of theceramic member 26 and a ceramic backing ring 30. The ceramic member 26has an internal diameter of 2.38 inches and a length of 3.0 inches.Within the ceramic member 26 there is housed coaxially a thin-walledtubular metal member 31. The inner end of the tubular member 31 liesjust within the compartment formed by the tubular member 2 and theflanges and 25, and at its outer end the tubular member 31 is providedwith an outwardly extending flange 32 which is sealed between the end ofthe ceramic member 26 and a relatively short tubular ceramic member 33.Half way along its length, the tubular member 31 is provided with anumber of outwardly projecting pips 34 which serve to locate the member31 within the ceramic member 26.

A further thin-walled tubular metal member 35 is disposed coaxiallywithin the tubular member 31, the inner end of the member 35 lying in aplane positioned about one third of the way along the length of thetubular member 31 in the direction towards the main body of theenvelope. At its outer end the tubular member is provided with anoutwardly extending ange 36 which is sealed between the end of theceramic member 33 and a backing ring 37.

The electrode system of the thyratron is housed within the main body ofthe envelope and comprises an anode 38, a control electrode 39, a baille40, a cathode 41, and an additional electrode 42, hereinafter referredto as the dummy anode.

The anode 38 is in the form of a disc of molybdenum which is housed justwithin the inner end of the tubular member 31 and is supported at oneend of a metal tube 52. The tube 52 extends away from the anode 38coaxially through the tubular member 31 to a plane about one third ofthe way along the length of the tubular member 35, the tube 52 beingsealed coaxially within the tubular member 35 where these two members 35and 43 overlap, thereby closing this end of the envelope.

The dummy anode is in the form of a thin copper disc secured to theinner end of the tubular member 31 so as to be disposed parallel to theanode 38 at a distance of 0.16 inch from the anode 38. In the centre ofthe dummy anode 42 there is formed a cross-shaped aperture 43, each ofthe four limbs of the aperture 43 having a width of 0.08 inch and alength of 0.89 inch.

Referring now to FIGURES 1 and 2, the control electrode 39 comprises acopper disc of thickness 0.15 inch which is sealed into the tubularenvelope member 2 so as to be disposed parallel to the dummy anode 42 ata distance of 0.16 inch from the dummy anode 42. The face of the controlelectrode 39 remote from the dummy anode 42 is recessed to provide acentral circular area 44 of diameter 2.0 inches and thickness 0.08 inch.In the area 44 there is formed centrally a cross-shaped aperture 45which is of thesame dimensions and is in register with the aperture 43in the dummy anode 42.

The bale 40 comprises a molybdenum disc of thickness 0.08 inch anddiameter 2.25 inches disposed within the longer tubular member 1 in aplane perpendicular to the axis of the envelope. The baie 40 is mounted,by means of a copper support 46 on and in good electric and thermalcontact with the flange 12 on the tubular member 1 at a distance of0.375 inch from the iiange 12.

The cathode 41 is also housed within the tubular member 1 and is of thetype described in the specification of my Patent No. 3,244,925. Thecathode 41 essentially comprises a hollow cylindrical member 47 -made ofelectron emitting material in which is housed an electric heater 48. Thecathode 41 is supported coaxially within a metal heat shield 49 which isgenerally tubular in shape and at its end remote from the anode 38 ismounted on the cup-shaped metal member 19.

The heat shield 49 is provided with a series of spaced rectangular fins50 which project radially inwards, the fins 50 being approximately thesame length as the Cathode 41. The internal surface of the heat shield49 and the surfaces of the fins 50 are coated with electron emissivematerialderived from the cathode 41, deposition of this Imaterial beingeffected during manufacture of the thyratron.

Connection to the control electrode 39 is made via the tubular member 2,connection to the cathode 41 and one end of the cathode heater -48 ismade via the metal member 19, connection to the other end of the cathodeheater 48 is made via a metal part o'f the envelope of thereplenisher'compartment 22 and connection to an electrical heatingelement (not shown) included in the replenisher is also made in thisway. Connection to the anode 38 is made via a threaded metal boss 51,and connection to the dummy anode is made via the tubular member 31.

In operation of the thyratron, a voltage of the order of 35 kilovolts isapplied between the anode 38 and the cathode 41, the anode 38 beingpositive with respect to the cathode 41, and the dummy anode 42 isconnected to the anode 38 via a resistor (not shown) of high value. Tohold the thyratron in a non-conducting condition the control electrode39 is maintained at substantially the same potential as the cathode 41,and the thyratron isiired by the application of a positive voltage pulseto the control electrode 39, the resulting discharge passing through theapertures 45 and 43 in the control electrode 39 and the dummy anode 42.

It will be appreciated that the presence of the high valued resistorbetween the anode 38 and the dummy anode 42 ensures that the dischargepasses to the anode 38 and not to the dummy anode 42.

When the thyratron is non-conducting, the dummy anode 42 issubstantially at the anode potential and the width of theaperture 43 inthe dummy anode 42 is suiiiciently small for the configuration of theelectric field on the cathode side of the dummy anode to be unaffectedby the shape of the surface of the anode 38. Thus, by virtue of thepresence of the dummy anode 42, deterioration of the performance of' thethyratron under hold-off conditions due to erosion of the anode 38 byhigh energy particles after a period of operation is to a large extentprevented whilst the performance of the thyratron when conducting issubstantially unaffected by the presence of the dummy anode 42. Thedummy anode 42 is not itself subject to erosion to any appreciableextent because the vast majority of the high energy particles causingerosion will pass through the aperture 43 in the dummy anode 42 and willtherefore not impinge on the surface of the dummy anode 42.

I claim:

1. An electric discharge device having a sealed envelope; a gas-fillingwithin the envelope, and an electrode structure within the envelope,said structure comprising: an anode, a cathode, a control electrode,disposed between the cathode and the anode, in which control electrodeis formed at least one elongated aperture through which the dischargebetween the anode and the cathode passes in operation, and an additionalelectrode which is disposed between the anode and the control electrode,which additional electrode is electrically insulated Afrom the controlelectrode and in which, for each said aperture in the control electrode,there is a corresponding aperture which is substantially the same shapeas the corresponding aperture in the control electrode and is at leastapproximately in register with the corresponding aperture in the controlelectrode with respect to the path of the discharge between the anodeand the control electrode, the width of each said aperture in theadditional electrode being suiliciently small substantially to preventpenetration of that aperture by electric field lines when the device isnon-conducting so that the configuration of the electric field on thecathode side of the additional electrode is unaffected by the shape ofthe surface of the anode.

Z. A device according to claim 1 wherein said additional electrode iselectrically insulated from all the other electrodes of the device.

3. A device according to claim 1 wherein said additional electrodecomprises an apertured planar metal member.

4. A device according to claim 1 wherein there is only one said aperturein the control electrode.

5. A device according to claim 4 wherein said aperture in the controlelectrode is cross-shaped.

6. An arrangement for operating an electric discharge device accordingto claim 1 including a resistive connection between the anode and saidadditional electrode so that when the discharge device is not conductingsaid additional electrode is at substantially the same potential as theanode, but when the discharge device is conducting the discharge passesto the anode rather than the additional electrode.

References Cited UNITED STATES PATENTS JAMES W. LAWRENCE, PrimaryExaminer R. F. HOSSFELD, Assistant Examiner U.S. C1. X.R. 313-193, 216,297

